
public class MyLinkedList {

    static class ListNode {
        public int val;
        public ListNode prev;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }

    //标记头
    public ListNode head;
    //标记尾
    public ListNode last;

    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            last = node;
        }else {
            node.next = head;
            head.prev = node;
            head = node;
        }
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            last = node;
        }else {
            last.next = node;
            node.prev = last;
            last = node;
        }
    }
    //任意位置插入,第一个数据节点为0号下标
    public void addIndex(int index,int data){
        int size = size();
        if(index < 0 || index > size) {
            System.out.println("下标位置不合法："+index);
            return;
        }
        if(index == 0) {
            addFirst(data);
            return;
        }
        if(index == size) {
            addLast(data);
            return;
        }
        ListNode node = new ListNode(data);
        ListNode cur = search(index);
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }

    private ListNode search(int index) {
        ListNode cur = head;
        while (index != 0) {
            cur = cur.next;
            index--;
        }
        return cur;
    }

    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
    //删除第一次出现关键字为key的节点
    public void remove(int key){
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key) {
                if(cur == head) {
                    //删除头节点
                    head = head.next;
                    if(head == null) {
                        //只有一个节点的情况下
                        last = null;
                    }else {
                        head.prev = null;
                    }
                }else {
                    //删除中间和尾巴
                    if(cur.next == null) {
                        //尾巴
                        cur.prev.next = cur.next;
                        last = last.prev;
                    }else {
                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;
                    }
                }
                return;
            }
            cur = cur.next;
        }
    }

    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key) {
                if(cur == head) {
                    //删除头节点
                    head = head.next;
                    if(head == null) {
                        //只有一个节点的情况下
                        last = null;
                    }else {
                        head.prev = null;
                    }
                }else {
                    //删除中间和尾巴
                    if(cur.next == null) {
                        //尾巴
                        cur.prev.next = cur.next;
                        last = last.prev;
                    }else {
                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;
                    }
                }
                //return;
            }
            cur = cur.next;
        }
    }

    //得到单链表的长度
    public int size(){
        ListNode cur = head;
        int count = 0;
        while (cur != null) {
            count++;
            cur = cur.next;
        }
        return count;
    }
    public void display(){
        ListNode cur = head;
        while (cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
        System.out.println();
    }

    public void clear(){
        ListNode cur = head;
        while (cur != null) {
            ListNode curN = cur.next;
            //cur.val = null;
            cur.prev = null;
            cur.next = null;
            cur = curN;
        }
        head = null;
        last = null;
    }
}
